102 PHYSIOLOGICAL SERIES. 



D. 114. The head of Mormyrus jubelini with the brain exposed 

 from the left side. In the Mormyridse the brain is re- 

 markable for the immense development of the valvula 

 eerehelli. Tlii> or ran does not lie as in other Teleosts 

 completely within the optic lobes, but projects through the 

 tectum opticum, thrusting its lateral parts downwards to 

 either side, and spreads out in three pairs of lobes or wings 

 over the surface of the brain, completely concealing it from 

 view when looked at from above, and extending so far down 

 on either side as to leave exposed only the lower parts of 

 the hemispheres and optic lobes. This unusual relation of 

 the valvula cerebelli to the tectum opticum appears to be a 

 further extension of some such process as that seen in the 

 I 'arp (D. 107), in which the lateral parts of the tectum are 

 divaricated and the central area much thinned out, but 

 without extrusion of the valvula. The wings of the valvula 

 an- ealled from their position anterior, lateral or middle, 

 and posterior. Their deep surface is occupied by a layer 

 of small cells (nuclear layer) covered superficially by a 

 number of parallel ridges each composed of molecular, 

 nuclear, intermediate, and fibrous layers. In the specimen 

 the exposed surface of the posterior wings has a finely 

 corrugated appearance duo to these ridges, but the anterior 

 and lateral wings are smooth, because, by folding, the deep 

 nuclear layer has become superficial in position. 



The olfactory bulbs are small and are situated close to 



the olfactory organs. They are connected by delicate 



peduncles to the cerebrum. The left basal ganglion can be 



seen below the anterior wing of the valvula ; it has a 



ome what oblong shape. Close behind it, below the anterior 



of the lateral wing of the valvula, lie t\v< narrow 



: I'ram-siiKstaiiee. The anterior of the two is the 



laterally depressed left half of the teeium opticum; the 



other is part of the torus semicircularis. 



Presented by J. S. Budgett, Esq. 



D. 115. The brain of Mormynis kanmtmc exposed in situ from 

 al'o\e. The \\injrsof the valvula cerebelli have been re- 



lllnM-d from the left H.le to e.\po>c the Underlying parts Of 



the brain. 



